The annual mean limit value is 40 µg NO2/m3. Over the years 2001-2010 the total population, for which exposure estimates are made, increased from 93 to 124 million people due to an increasing number of monitoring stations reporting air quality data under the Exchange of Information Decision. Year-to-year variations in exposure classes are partly caused by the changes in spatial coverage. Only urban and sub-urban background monitoring stations have been included in the calculations. Data for Cyprus, Greece and Malta, are not included due to missing availability of operational urban and sub-urban background monitoring stations in the Urban Audit cities.

Particulate Matter (PM 10 ) In the period 1997-2008, 18-50 % of the urban population was potentially exposed to ambient air concentrations of particulate matter (PM 10 ) in excess of the EU limit value set for the protection of human health (50 microgram /m 3 daily mean not be exceeded more than 35 days a calendar year); (Figure 1). Nitrogen dioxide (NO 2 ) In the period 1997-2008, 6-41 % of the urban population was potentially exposed to ambient air nitrogen dioxide (NO 2 ) concentrations above the EU limit value set for the protection of human health (40 microgram NO 2 /m 3 annual mean). There was a slight downwards trend over the period (Figure 1). Ozone (O 3 ) In the period 1997-2008, 13-62 % of the urban population in Europe was exposed to ambient ozone concentrations exceeding the EU target value set for the protection of human health (120 microgram O 3 /m 3 daily maximum 8-hourly average, not to be exceeded more than 25 times a calendar year by 2010). The 62 % of the urban population exposed to ambient ozone concentrations over the EU target value was recorded in 2003, which was the record year. There was no discernible trend over the period (Figure 1). Sulphur dioxide (SO 2 ) In the period 1997-2008, the fraction of the urban population in EEA-32 member countries that is potentially exposed to ambient air concentrations of sulphur dioxide in excess of the EU limit value set for the protection of human health (125 microgram SO 2 /m 3 daily mean not to be exceeded more than three days a year), decreased to less than 1 %, and as such the EU limit value set is close to being met everywhere in the urban background (Figure 1).